1. Field
Example embodiments of the following description relate to an image forming apparatus and method, and more specifically, an image forming apparatus and method that may securely mix a toner and a carrier in a minimum space when high-speed printing is performed.
2. Description of the Related Art
Image forming apparatuses using electrophotography, such as laser printers, laser fax machines, or digital copiers, charge a photosensitive drum and expose the photosensitive drum to thus form an electrostatic latent image in accordance with an image signal. Then, the image forming apparatus supplies a toner charged by a developing unit to the photosensitive drum to develop the electrostatic latent image, transfer the developed image onto a printing medium, such as a paper, and fuse the image by using a fusing unit, thereby forming an image.
It is well known that, in image forming apparatuses, a magnet roller is used for supplying a toner to the photosensitive drum. For example, Japanese Patent Application Publication No. hei 10-142916 and Japanese Patent Application Publication No. 2006-323238 that are described as prior art references in the background of the disclosure disclose an apparatus using a two-component developing agent containing a toner and a carrier. Also, Japanese Patent Application Publication No. hei 10-142916 discloses a configuration for supplying a toner by mixing the toner in a developing agent.
The processing capability of image forming apparatuses has recently increased, and thus, the number of pages that can be printed per unit time has greatly increased. Thus, in apparatuses using a two-component developing agent, the amount of consumed toner is continually supplemented, and simultaneously, the supplemented toner and carrier need to be mixed within a short time.
However, in image forming apparatuses according to the related arts described above, high-speed printing is not considered. Thus, when the amount of consumed toner is supplemented and is supplied, the toner and the carrier may not be sufficiently mixed due to high-speed printing.
In particular, the demand for relatively small image forming apparatuses that print A4 paper is increasing. In such small image forming apparatuses, the length of a path in which the toner is received or transferred, is also decreased. Thus, a distance at which the toner and the carrier are agitated is also decreased, so that a toner/carrier mixture is insufficient.
When the toner/carrier mixture is insufficient, the toner friction charges the carrier, and the toner having an appropriate polarity and an appropriate amount of charge cannot be controlled. Thus, the quality of an image may be lowered due to the toner having an opposite polarity and a small amount of charge.
In addition, the amount of a developing agent is decreasing as the size of image forming apparatuses is reduced. In particular, for low cost per page and for enhancing quality of a printed image, the concentration of an image can be maintained only with a small amount of developing agent by adding a strong pigment to the toner and decreasing the diameter of the carrier. However, in systems using a two-component developing agent, the amount of consumed toner is precisely measured, is injected into the carrier, is agitated, charged, and dispersed. To this end, an agitation time is required. When the agitation time is short, the toner is not sufficiently charged and is not deposited on the surface of the carrier and is received or transferred from/to a developing region.
In addition, the developing agent uses powder that is coated with resin on the surface of ferrite or magnetite, and the toner of which a main ingredient is resin is mixed with the powder. Thus, when the toner is mixed in the flow of the developing agent, there is a difference in specific gravity between the toner and the developing agent and the toner is not smoothly mixed with the flow of the developing agent. Thus, the toner may be received or transferred from/to the developing region with insufficient charge and dispersion. Basically, the toner having an appropriate polarity and an appropriate amount of charge needs to be controlled. When charge/dispersion is insufficient, the toner can have an opposite polarity and the amount of charge of the toner can be lowered. Thus, the toner attaches to a region of a photosensitive drum to which the toner is not to attach, thus deteriorating the quality of an image (background pollution of the image is increased) and image contamination occurs. In addition, when the amount of charge of the toner is insufficient, contamination may occur in the developing unit. In particular, in the case of a high-speed developing unit for A4 paper, the agitation time is 25% shorter than in a developing unit for A3 paper. Thus, there is a limitation in realizing a high speed in general developing units.